Low-temperature hydrogen production from oxygenated hydrocarbons

ABSTRACT

Disclosed is a method of producing hydrogen from oxygenated hydrocarbon reactants, such as glycerol, glucose, or sorbitol. The method can take place in the vapor phase or in the condensed liquid phase. The method includes the steps of reacting water and a water-soluble oxygenated hydrocarbon having at least two carbon atoms, in the presence of a metal-containing catalyst. The catalyst contains a metal selected from the group consisting of Group VIII transitional metals, alloys thereof, and mixtures thereof. The disclosed method can be run at lower temperatures than those used in the conventional steam reforming of alkanes.

FEDERAL FUNDING STATEMENT

This invention was made with United States government support awarded byNSF Grant No. 9802238 and DOE Grant No. DE-FG02-84ER13183. The UnitedStates has certain rights in this invention.

FIELD OF THE INVENTION

The invention is directed to a method of producing hydrogen (H2) byvapor- and condensed liquid-phase reforming of oxygenated hydrocarbons.

BACKGROUND OF THE INVENTION

Fuel cells have emerged as one of the most promising new technologiesfor meeting future global energy needs. In particular, fuel cells thatconsume hydrogen are proving to be environmentally clean, quiet, andhighly efficient devices for power generation. However, while hydrogenfuel cells have a low impact on the environment, the current methods forproducing hydrogen require high-temperature steam reforming ofnon-renewable hydrocarbon fuels. Further still, these high-temperaturemethods produce significant amounts of polluting emissions andgreenhouse gases such as carbon dioxide (CO₂).

A key challenge for promoting and sustaining the vitality and growth ofthe fuel cell industry (as well as the entire industrial sector ofsociety) is to develop efficient and environmentally benign technologiesfor generating fuel, such as hydrogen, from renewable resources.Notably, if hydrogen fuel for consumption in fuel cells can be generatedefficiently from renewable sources, then non-renewable resources such aspetroleum feedstocks can be used for other, more beneficial, and lessenvironmentally deleterious purposes. Moreover, the generation of energyfrom renewable resources such as biomass, reduces the net rate ofproduction of carbon dioxide, an important greenhouse gas thatcontributes to global warming. This is because the biomass itself, i.e.,plant material, consumes carbon dioxide during its life cycle.

At present, the vast majority of hydrogen production is accomplished viasteam reforming of a hydrocarbon (usually methane) over a suitablecatalyst. Conventional steam reforming takes place at considerablyelevated temperatures, generally from about 400° C. to 700° C. or evenhigher (673 to 937 K and higher).

The net desired steam reformation reaction of a hydrocarbon is shown inreaction (1). The reaction requires a catalyst, conventionally anickel-based catalyst on a modified alumina support.

C_(x)H_(2x+2) +xH₂O→xCO+(2x+1)H₂  (1)

The nickel catalyst is sensitive to sulfur poisoning, which can beproblematic. Hydrocarbon feedstocks produced from petroleum contain asignificant amount of sulfur. Therefore, the hydrocarbon reactants musthave the contaminating sulfur removed prior to undergoing steamreforming.

Conventional steam reforming is generally followed by one or morewater-gas shift (WGS) reactions (reaction (2)) that take place in asecond and perhaps a third reactor.

CO+H₂O→CO₂+H₂  (2)

The WGS reaction uses steam to convert the carbon monoxide produced inreaction (1) to carbon dioxide and hydrogen. The WGS reaction is thusused to maximize the production of hydrogen from the initial hydrocarbonreactants.

An entire, and typical, prior art process for the steam reformation ofmethane is illustrated schematically in FIG. 1. The hydrocarbonfeedstock is first desulfurized at 10. The desulfurized feedstock isthen subjected to a first high-temperature, vapor-phase reformingreaction in a first high-temperature reaction chamber at 12. As notedearlier, this reaction generally uses a nickel-based catalyst. Theproducts of the reaction at 12 are then swept into a second reactor fora first WGS reaction 14. This first WGS reaction takes place atapproximately 300° C. to 350° C., using an iron catalyst. The productsof the reaction at 14 are swept into a third reactor for a second WGSreaction 16. This second WGS reaction takes place a reduced temperatureof from about 200° C. to 250° C. The products of the reaction at 16 arethen passed through a separator 18, where the products are separatedinto two streams: CO₂ and H₂O(the water which is pumped back into thereaction cycle at the beginning) and CO and H₂. The CO and H₂ streamfrom the separator 18 may also be subjected (at 20) to a finalmethanation reaction (to yield CH₄ and H₂) or an oxidation reaction toyield CO₂ and H₂.

It has been reported that it is possible to produce hydrogen via steamreformation of methanol at temperatures near 277° C. (550 K). See B.Lindstrom & L. J. Pettersson, Int. J Hydrogen Energy 26(9), 923 (2001),and J. Rostrup-Nielsen, Phys. Chem. Chem. Phys. 3, 283 (2001). Theapproach described in these references uses a copper-based catalyst.These catalysts, however, are not effective to steam reform heavierhydrocarbons because the catalysts have very low activity for cleavageof C—C bonds. Thus, the C—C bonds of heavier hydrocarbons will not becleaved using these types of catalysts.

Wang et al., Applied Catalysis A: General 143, 245-270 (1996), report aninvestigation of the steam reformation of acetic acid andhydroxyacetaldehyde to form hydrogen. These investigators found thatwhen using a commercially available nickel catalyst (G-90C from UnitedCatalysts Inc, Louisville, Ky.), acetic acid and hydroxyacetaldehyde canbe reformed to yield hydrogen in high yield only at temperatures at orexceeding 350° C. Importantly, the nickel catalyst was observed todeactivate severely after a short period of time on stream.

A hydrogen-producing fuel processing system is described in U.S. Pat.No. 6,221,117 B1, issued Apr. 24, 2001. The system is a steam reformerreactor to produce hydrogen disposed in-line with a fuel cell. Thereactor produces hydrogen from a feedstock consisting of water and analcohol (preferably methanol). The hydrogen so produced is then fed asfuel to a proton-exchange membrane (PEM) fuel cell. Situated between thereactor portion of the system and the fuel cell portion is ahydrogen-selective membrane that separates a portion of the hydrogenproduced and routes it to the fuel cell to thereby generate electricity.The by-products, as well as a portion of the hydrogen, produced in thereforming reaction are mixed with air, and passed over a combustioncatalyst and ignited to generate heat for running the steam reformer.

Conventional steam reforming has several notable disadvantages. First,the hydrocarbon starting materials contain sulfur which must be removedprior to steam reformation. Second, conventional steam reforming must becarried out in the vapor phase, and high temperatures (greater than 500°C.) to overcome equilibrium constraints. Because steam reformation usesa considerable amount of water which must also be heated tovaporization, the ultimate energy return is far less than ideal. Third,the hydrocarbon starting materials conventionally used in steamreforming are highly flammable. The combination of high heat, highpressure, and flammable reactants make conventional steam reforming areasonably risky endeavor.

Thus, there remains a long-felt and unmet need to develop a method forproducing hydrogen that utilizes low sulfur content, renewable, andperhaps non-flammable starting materials. Moreover, to maximize energyoutput, there remains an acute need to develop a method for producinghydrogen that proceeds at a significantly lower temperature thanconventional steam reforming of hydrocarbons derived from petroleumfeedstocks. Lastly, there remains a long-felt and unmet need to simplifythe reforming process by developing a method for producing hydrogen thatcan be performed in a single reactor.

SUMMARY OF THE INVENTION

The invention is directed to a method of producing hydrogen via thereforming of an oxygenated hydrocarbon feedstock. The method comprisesreacting water and a water-soluble oxygenated hydrocarbon having atleast two carbon atoms, in the presence of a metal-containing catalyst.The catalyst comprises a metal selected from the group consisting ofGroup VIII transitional metals, alloys thereof, and mixtures thereof.

In a first embodiment of the invention, the water and the oxygenatedhydrocarbon are reacted at a temperature of from about 100° C. to about450° C. More preferably, the reaction takes place at a temperature offrom about 100° C. to about 300° C. In either instance, the reaction isrun at a pressure where the water and the oxygenated hydrocarbon aregaseous.

In a second embodiment of the invention, the water and the oxygenatedhydrocarbon are reacted at a temperature not greater than about 400° C.and at a pressure where the water and the oxygenated hydrocarbon remaincondensed liquids.

In the second embodiment, it is preferred that the water and theoxygenated hydrocarbon are reacted at a pH of from about 4.0 to about10.0.

In both the first and second embodiments, it is preferred that thecatalyst comprise a metal selected from the group consisting of nickel,palladium, platinum, ruthenium, rhodium, iridium, alloys thereof, andmixtures thereof. Optionally, the catalyst may also be further alloyedor mixed with a metal selected from the group consisting of Group IBmetals, Group IIB metals, and Group VIIb metals, and from among these,preferably copper, zinc, and/or rhenium. It is also much preferred thatthe catalyst be adhered to a support, such as silica, alumina, zirconia,titania, ceria, carbon, silica-alumina, silica nitride, and boronnitride. Furthermore, the active metals may be adhered to a nanoporoussupport, such as zeolites, nanoporous carbon, nanotubes, and fullerenes.

The support itself may be surface-modified to remove, cap, or otherwisemodify surface moieties, especially surface hydrogen and hydroxylmoieties that may cause localized pH fluctuations. The support can besurface-modified by treating it with silanes, alkali compounds, alkaliearth compounds, and the like. A preferred modified support is silicathat has been treated with trimethylethoxysilane.

In the second embodiment of the invention, where the water and theoxygenated hydrocarbon remain condensed liquids, the method can alsofurther comprise reacting the water and the water-soluble oxygenatedhydrocarbon in the presence of a water-soluble salt of an alkali oralkali earth metal. The addition of these salts tends to increase theoverall production of hydrogen realized in the method. It is preferredthat the water-soluble salt is an alkali or an alkali earth metalhydroxide, carbonate, nitrate, or chloride salt. Potassium hydroxide(KOH) is preferred.

In both the first and second embodiments, it is much preferred that thewater-soluble oxygenated hydrocarbon has a carbon-to-oxygen ratio of1:1. Particularly preferred oxygenated hydrocarbons include ethanediol,ethanedione, glycerol, glyceraldehyde, aldotetroses, aldopentoses,aldohexoses, ketotetroses, ketopentoses, ketohexoses, and alditols. Fromamong the oxygenated hydrocarbons having six carbon atoms, glucose andsorbitol are preferred. Ethanediol, glycerol, and glyceraldehyde are thepreferred oxygenated hydrocarbons from among those having less than sixcarbon atoms.

The invention will also function with mixed feedstocks of oxygenatedhydrocarbons, that is, feedstocks containing mixtures of two or moreoxygenated hydrocarbons.

The present invention thus provides methods for producing hydrogen via alow-temperature, catalytic reforming of oxygenated hydrocarbon compoundssuch as ethanediol, glycerol, sorbitol, glucose, and other water-solublecarbohydrates. For the purpose of the present invention, “reforming” or“steam reforming” is defined as the reaction of an oxygenatedhydrocarbon feedstock to yield hydrogen and carbon dioxide.

A principal advantage of the subject invention is that the oxygenatedhydrocarbon reactants can be produced from renewable resources, such asbiomass. Thus, the present method can be used to generate a fuel source,namely hydrogen, from an abundant and fully renewable source. Also,because living plant matter consumes carbon dioxide, the use of thesefeedstocks in power generation applications does not result in a netincrease of carbon dioxide vented to the atmosphere.

Another equally important advantage of the present method is that itfunctions at a much lower temperature than conventional steam reformingof hydrocarbons. Conventional steam reforming of hydrocarbons requiresoperating temperatures greater than about 500° C. (773 K). The subjectmethod, however, is able reform aqueous solutions or gaseous mixtures ofoxygenated hydrocarbons to yield hydrogen, at temperatures of from about100° C. to about 450° C. in the vapor phase. More preferably still, thevapor phase reaction is run at a temperature of from about 100° C. toabout 300° C. In the condensed liquid phase, the reaction is run attemperatures not greater than about 400° C.

Another beneficial aspect of. the present invention is that it allowsfor the reforming of the oxygenated hydrocarbon and a simultaneous WGSreaction to take place in a single reactor.

Another distinct advantage of the present invention is that oxygenatedhydrocarbons are far less dangerous than are the conventionalhydrocarbons normally used in steam reformation. Thus, the presentinvention yields hydrogen from such relatively innocuous substances asethanediol, glycerol, glucose, and sorbitol (as compared to the highlyflammable methane or propane that are used in conventional reformingmethods).

Still another advantage of the present invention is that when the methodis carried out in the condensed liquid phase, it eliminates the need tovaporize water to steam. This is a critical concern in large-scaleoperations due to the high energy costs required to vaporize largeamounts of water. The heat of vaporization of water is more than 2000 kJper mole. By eliminating the need to vaporize the water, the amount ofenergy that must be input into the claimed method to yield hydrogen isgreatly reduced. The overall energy yield, therefore, is concomitantlyincreased.

Thus, the subject method provides a means to convert oxygenatedhydrocarbons to yield hydrogen, using a single reactor bed and reactorchamber, and at low temperatures. Such a reactor system can befabricated at a reduced volume and can be used to produce hydrogen thatis substantially free of contaminates for use in portable fuel cells orfor use in applications in remote locations.

The hydrogen produced using the present invention can be utilized in anyprocess where hydrogen is required. Thus, the hydrogen can be used, forexample, as a fuel for fuel cells. The hydrogen can be used forproducing ammonia, or it could be used in the refining of crude oil. Themethod yields a hydrogen stream that has a very low sulfur content. Whenlow sulfur content reactants are utilized, the method yields a hydrogenstream that is substantially free of both sulfur and carbon monoxide.This type of hydrogen stream is highly suitable for use in fuel cells,where sulfur and/or carbon monoxide can poison the catalysts located atthe electrodes of each fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a PRIOR ART method of steam reforming ahydrocarbon feedstock to yield hydrogen.

FIG. 2 is a graph depicting the thermodynamics for the conversion ofhydrocarbons and oxygenated hydrocarbons to carbon monoxide and hydrogen(H₂).

FIG. 3 is a graph depicting, on the same temperature scale, thethermodynamics for the conversion of oxygenated hydrocarbons to carbonmonoxide and H₂, and the vapor pressures of the oxygenated hydrocarbonreactants as a function of temperature.

FIG. 4 is a graph depicting the temperature at which ΔG°/RT is equal tozero versus the number of carbons in the reactants for the steamreforming alkanes (trace 10) and oxygenated hydrocarbons (trace 12)having a carbon-to-oxygen ratio of 1:1. This figure also includes a plot(trace 14) of the temperature at which the vapor pressure of theoxygenated hydrocarbons is equal to 0.1 atm.

FIG. 5 is a schematic diagram of a reactor system that can be used tocarry out the condensed liquid phase reforming of oxygenatedhydrocarbons.

FIG. 6 is a schematic diagram of a one-reactor approach for reformingoxygenated hydrocarbons into CO and H₂, followed by a WGS reaction tomaximize the production of H₂.

FIG. 7 shows the vapor-phase reforming of ethanediol over a 4 wt %Ru/SiO₂ catalyst system at 300° C. and 1 atm as detailed in Example 7.

FIG. 8 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, and a molar water-to-carbon ratio of 15 over mono-metallic catalystsystems containing Rh, Ni, Ru, Ir, Co, or Fe, as detailed in Example 9.

FIG. 9 shows vapor-phase reforming of ethanediol at 250° C. and 1 atm,and a water-to-carbon molar ratio of 15 over two different nickelcatalyst systems (1 wt % Ni/SiO₂ and 15 wt % Ni/MgO—Al₂O₃), as detailedin Example 9.

FIG. 10 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, and a water-to-carbon ratio of 15 over a bimetallic catalyst system(Ni—Pd) as compared to monometallic Rh/SiO₂, Pd, and Ni catalystsystems, as detailed in Example 9.

FIG. 11 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, and a water-to-carbon ratio of 15 over various catalyst systems(Rh, Ni—Pt, Pt, and Ni), as detailed in Example 9.

FIG. 12 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, and a water-to-carbon ratio of 15 over various catalyst systems(Rh, Ru—Pd, Pd, and Ru), as detailed in Example 9.

FIG. 13 shows the vapor-phase reforming of sorbitol at 425° C. and 1atm, at a water-to-carbon ratio of 32 over silica-supported rhodiumcatalyst systems as detailed in Example 10.

FIG. 14 shows the vapor-phase reforming of sorbitol at 425° C. and 1atm, at a water-to-carbon ratio of 32 over silica-supported rhodiumcatalyst systems as detailed in Example 10, in the presence and absenceof added helium.

FIG. 15 shows the results for the condensed liquid phase reforming of a10 wt % sorbitol solution over a 5 wt % Pt/SiO₂ catalyst system at 225°C., followed by liquid phase reforming of a 10 wt % glucose solution.See Example 12.

FIG. 16 shows the condensed liquid phase reforming of a 10 wt % sorbitolsolution over a modified 5 wt % Pt/SiO₂ catalyst system. See Examples 11and 12.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an energy efficient method for steam reformingoxygenated hydrocarbons at considerably lower temperatures thanpreviously possible. The reaction can take place in the vapor phase, inthe same fashion as conventional steam reforming reactions (although ata much lower temperature). The reaction can also take place in thecondensed liquid phase, in which case the reactants (water and anoxygenated hydrocarbon) remain condensed liquids, as opposed to beingvaporized prior to reaction.

As used herein to describe the present invention, the terms “reforming,”“steam reforming,” and “steam reformation” are synonymous. These termsshall generically denote the overall reaction of an oxygenatedhydrocarbon and water to yield a hydrogen stream, regardless of whetherthe reaction takes place in the gaseous phase or in the condensed liquidphase. Where the distinction is important, it shall be so noted.

When the steam reforming of oxygenated hydrocarbons is carried out inthe liquid phase, the present invention makes it possible to producehydrogen from aqueous solutions. of oxygenated hydrocarbons havinglimited volatility, such as glucose and sorbitol.

Abbreviations and Definitions:

“GC”=gas chromatograph or gas chromatography.

“GHSV”=gas hourly space velocity.

“psig”=pounds per square inch relative to atmospheric pressure (i.e.,gauge pressure).

“Space Velocity”=the mass/volume of reactant per unit of catalyst perunit of time.

“TOF”=turnover frequency.

“WHSV”=weight hourly space velocity=mass of oxygenated compound per massof catalyst per h.

“WGS”=water-gas shift.

Thermodynamic Considerations:

As noted above, the stoichiometric reaction for steam reforming ofalkanes to yield hydrogen and carbon monoxide is given by reaction (1):

C_(x)H_(2x+2) +xH ₂O→xCO+(2x+1)H₂  (1)

The stoichiometric reaction for steam reforming of carbon monoxide toyield hydrogen and carbon dioxide is given by the water-gas shift (WGS)reaction, reaction (2):

CO+H₂O→CO₂+H₂  (2)

The stoichiometric reaction for steam reforming of an oxygenatedhydrocarbon having a carbon-to-oxygen ration of 1:1 is given by reaction(3):

C_(x)H_(2y)O_(x) →nCO+yH₂  (3)

FIG. 2 is a graph depicting the changes in the standard Gibbs freeenergy (ΔG°) associated with reaction (1) and (3) for a series ofalkanes (CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, and C₆H₁₄) and oxygenatedhydrocarbons having a carbon-to-oxygen ratio of 1:1 (CH₃OH, C₂H₄(OH)₂,C₃H₅(OH)₃, and C₆H₈(OH)₆). The values plotted in FIG been normalized permole of CO. The ΔG° data points shown in FIG. 2 have been divided by RT.Thus, FIG. 2 is a plot having ΔG°/RT on the Y-axis and temperature (inKelvins) on the X-axis. It can be seen from FIG. 2 that the steamreforming of C₁ to C₆ alkanes to produce CO and H₂ is thermodynamicallyfavorable (i.e., ΔG° is negative) at significantly higher temperaturesthan those required for the steam reforming of the oxygenatedhydrocarbons having the same number of carbon atoms.

For example, the steam reforming of methane, trace 10 in FIG. 2, becomesthermodynamically favorable only at temperatures above about 900 K. Incontrast, the steam reforming of the oxygenated hydrocarbons (traces 14,16, 18, 20, and 22) is favorable at temperatures above about 400 K.

Reactions (4) and (5) represent the reforming of CH₂ groups in alkanesas compared to CH(OH) groups in oxygenated hydrocarbons:

C₃H₈+H₂O→C₂H₆+CO+2H₂  (4)

C₃H₈O₃→C₂H₆O₂+CO+H₂  (5)

The value of ΔG°/RT for reaction (4), involving CH₂ groups, is equal tozero at a temperature of about 635 K. In contrast, ΔG°/RT for reaction(5), involving CH(OH) groups, is equal to zero at a temperature of about320 K. Thus, according to the present invention, the steam reforming ofoxygenated hydrocarbons, especially hydrocarbons having acarbon-to-oxygen ratio of 1:1 (the preferred ratio) is thermodynamicallyfavorable at temperatures far lower than the analogous steam reformingreaction of alkanes.

FIG. 2 also shows that the value of ΔG° for the WGS reaction (reaction(3), trace 12 of FIG. 2) is more favorable at lower temperatures. Thisreveals that the conversion of CO (produced in reactions (1) and (2)) toCO₂ and H₂ is more favorable at the lower temperatures associated withthe reforming of oxygenated hydrocarbons. Therefore, the steam reformingof oxygenated hydrocarbons provides a low-temperature route to theformation of CO₂ and H₂, provided that appropriate catalysts aredeveloped for operation at these low temperature reaction conditions.

As a general proposition (albeit with several exceptions), the rate ofcleavage of C—H bonds on metal surfaces is faster than the cleavage ofC—C bonds on metal surfaces. Accordingly, the steam reforming of, forexample, methanol to produce CO and H₂, would be expected to berelatively facile compared to the reforming of ethanediol (i.e.,ethylene glycol) to yield the same product mix. In the case of methanol,the general proposition holds true: The steam reforming of methanol canbe achieved at low temperatures over catalysts (such as copper) that donot readily cleave C—C bonds. In contrast, the steam reforming ofethanediol will not readily take place under these conditions using thesame copper catalysts because the catalyst does not effectively catalyzethe cleavage of C—C bonds.

Also, because methanol itself is typically produced from a CO and H₂stream that is derived from petroleum processing, the steam reforming ofmethanol does not represent the production of energy from a renewableresource. For this reason, appropriate catalysts for use in the presentinvention must show good activity for the cleavage of C—C bonds.

The thermodynamic trends shown in FIG. 2 also indicate that appropriatecatalysts for use in the present invention must not show high activityfor the cleavage of C—O bonds. Consider, for example, the steamreforming of ethanediol, reaction (6), followed by cleavage of the C—Obond in carbon monoxide to form methane and water, reaction (7), leadingto the overall process given by reaction (8):

C₂H₄(OH)₂ → 2 CO + 3 H₂ ΔG°/RT = −14 (at 470 K) (6) CO + 3 H₂ → CH₄ +H₂O ΔG°/RT = −26 (at 470 K) (7) C₂H₄(OH)₂ → CO + CH₄ + H₂O ΔG°/RT = −40(at 470 K) (8)

Because reaction (7) is the reverse of the steam reforming of methane,it is apparent from FIG. 2 that reaction (7) becomes very favorable atlow temperatures. Thus, for example, at a temperature of 470 K, thevalues of ΔG°/RT for reactions (6) and (7) are equal to −14 and −26,respectively. This leads to a very favorable ΔG°/RT value of −40 for theoverall reaction (8). Therefore, a reforming catalyst that is readilyable to cleave C—C and C—O bonds would convert ethanediol at lowtemperatures to a mixture of CO and CH₄, instead of the desired productmixture of CO and H₂. The CO and H₂ product mixture is preferred becauseit is followed by the production of CO₂ and H₂ by the WGS reaction.Clearly then, the production of CH₄ is undesirable for a fuel cellapplication because the production of CH₄ creates a significant loss ofH₂ from the system.

The above behavior for steam reforming of oxygenated hydrocarbons havinga carbon-to-oxygen ratio of 1:1 can be extended to the reforming at lowtemperatures of oxygenated hydrocarbons having a carbon-to-oxygen ratiohigher than 1:1. In particular, upon reforming, these oxygenatedhydrocarbons having higher carbon-to-oxygen ratios yield CO and H₂, plusthe formation of the appropriate alkane. For example, consider theconversion of ethanol according to the following reaction:

C₂H₅OH→CO+H₂+CH₄ ΔG°/RT=−16 (at 470 K)  (9)

It can be seen from in FIG. 2, trace 22, that reaction (9) is veryfavorable at low temperatures. At 470 K, the value of ΔG°/RT forreaction (9) is equal to −16. Thus, according to the present invention,a catalyst is used to convert ethanol at low temperatures to produce H₂(which can be used for any purpose, such as to power a fuel cell) and toco-generate methane for some other application (such as a combustionprocess to produce heat). To achieve this co-generation operation,however, it is necessary that the catalyst does not facilitate thereaction of ethanol with H₂ to produce ethane:

C₂H₅OH+H₂→C₂H₆+H₂O ΔG°/RT=−16(at 470 K)  (10)

As noted, at 470 K, the value of ΔG°/RT for reaction (10) is −24, avalue more negative than that for reaction 9. This again demonstratesthe importance that the catalyst to be used in the present inventionshould not show high activity for the cleavage of C—O bonds.

Vapor-Phase Reforming vs. Condensed Liquid-Phase Reforming:

The steam reforming of hydrocarbons typically takes place in the vaporphase. Therefore, the vapor-phase steam reforming at low temperatures ofoxygenated hydrocarbons may (under certain circumstances) be limited bythe vapor pressure of the reactants. FIG. 3 is a graph that depicts, onthe same temperature scale, the vapor pressure of various oxygenatedhydrocarbons as a function of temperature and the thermodynamics ofthese same oxygenated hydrocarbons in the reforming reaction yielding COand H₂. The upper portion of FIG. 3 shows plots of the vapor pressure(atm) versus temperature (K) for oxygenated hydrocarbons having acarbon-to-oxygen ratio of 1:1 (CH₃OH, C₂H₄(OH)₂, C₃H₅(OH)₃, andC₆H₈(OH)₆). The lower portion of FIG. 3 shows plots of ΔG°/RT versustemperature for these same reactants.

In evaluating FIG. 3, assume (for sake of simplicity) that the vaporpressure of the hydrocarbon reactant should be higher than about 0.1 atmfor economically-feasible vapor-phase steam reforming. Thus, as it canbe seen in FIG. 3, low-temperature steam reforming of methanol (vaporpressure=trace 10, ΔG°/RT=trace 12) is not fundamentally limited by thevapor pressure of the methanol reactant, but is fundamentally limited bythe value of ΔG°/RT for the corresponding stoichiometric reaction. Thisis because a vapor pressure of 0.1 atm of methanol is achieved at alower temperature (290 K) than the temperature at which ΔG°/RT becomesequal to zero (410 K). Thus, at the temperature where ΔG°/RT becomesfavorable for the steam reforming of methanol (410 K), the methanol isalready entirely vaporized.

In contrast, the vapor-phase steam reforming of heavier oxygenatedhydrocarbons may be limited by the vapor pressure of these reactants.For example, it can be seen in FIG. 3 that the vapor-phase steamreforming of ethanediol (traces 14 and 16) and glycerol (traces 18 and20) should be carried out at temperatures higher than about 400 K and500 K, respectively. In contrast to these moderate temperatures, thevapor-phase steam reforming of sorbitol must be carried out attemperatures higher than about 700 K, a temperature at which the vaporpressure of sorbitol is roughly 0.1 atm.

FIG. 4 is a graph depicting the temperature (K, on the Y-axis) at whichΔG°/RT is equal to zero versus the number of carbons in the reactantsfor the steam reforming alkanes (trace 10) and oxygenated hydrocarbons(trace 12) having a carbon-to-oxygen ratio of 1:1. This figure alsoincludes a plot (trace 14) of the temperature at which the vaporpressure of the oxygenated hydrocarbons is equal to 0.1 atm. As shown inFIG. 3, the plots superimposing ΔG°/RT and vapor pressure intersect atcarbon numbers between 1 and 2 for these oxygenated hydrocarbons (thatis, between methanol and ethanediol). A close analysis of FIG. 4indicates the following points: (1) the vapor-phase reforming ofmethanol (1 carbon atom) can be carried out at temperatures that arelower by about 500 K as compared to methane; (2) the vapor-phasereforming of ethanediol (2 carbon atoms) can be carried out attemperatures that are lower by about 340 K as compared to ethane; and,(3) the vapor-phase reforming of glycerol (i.e., propanetriol, 3 carbonatoms) can be carried out at temperatures that are lower by about 230 Kas compared to propane.

In contrast to these lighter oxygenated hydrocarbons, the vapor-phasereforming of sorbitol (6 carbon atoms) must be carried out attemperatures that are similar to those for hexane, roughly 680 to 700 K.Thus, there is a tremendous energy advantage in vapor-phase reforming ofshort-chain oxygenated hydrocarbons as compared to the correspondingalkanes. The advantage in operating at lower temperatures forvapor-phase reforming of lighter oxygenated hydrocarbons compared toreforming of alkanes having the same carbon number is actually even moresignificant than as presented in FIG. 4. In particular, the values ofΔG°/RT used to construct plots 10 and 12 of FIG. 4 do not take intoaccount the WGS reaction. That is, the ΔG°/RT values plotted in FIG. 4assume that the product mixture is H₂ and CO, rather than CO₂. In otherwords, the ΔG°/RT values shown in FIG. 4 do not account for a subsequentWGS reaction, which will result in the production of still morehydrogen. As discussed above, the WGS reaction is more favorable at thelower temperatures appropriate for the steam reforming of oxygenatedhydrocarbons. Thus, steam reforming of oxygenated hydrocarbons is a farmore efficient reaction than the steam reforming reaction using thecorresponding alkane.

The thermodynamic considerations summarized in FIG. 4 show that it ispossible to conduct the vapor-phase steam reforming of methanol,ethanediol and glycerol at significantly lower temperatures as comparedto the corresponding alkanes having the same number of carbon atoms.

While this low-temperature advantage does not exist for the vapor-phasesteam reforming of sorbitol, unlike hexane, sorbitol is readily obtainedfrom a renewable resource (i.e., glucose). In contrast, hexane isderived from non-renewable petroleum. Therefore, the vapor-phase steamreforming of sorbitol has very important environmental and long-term useadvantages as compared to using hexane.

Another aspect of the invention also is revealed by a close inspectionof FIG. 4 and that is that the advantages of producing H₂ from steamreforming of sorbitol can be achieved more fully by conducting thereaction in the condensed liquid phase. By conducting the reformingreaction in the condensed liquid phase, rather than the gas phase, theneed to vaporize the reactant is eliminated. (Thus, the energy requiredto surmount the heat of vaporization of the reactants is likewiseeliminated.) In the case of sorbitol in particular, liquid-phasereforming of sorbitol can be carried out at a temperature that isroughly 360 K lower than the temperature required to reform hexane inthe condensed liquid phase.

Using reforming of oxygenated hydrocarbons (either in the vapor phase orthe condensed liquid phase), it becomes possible to produce H₂ fromcarbohydrate feedstocks, such as glucose and corn starch, that havelimited volatility. For example, the reforming of glucose would proceedaccording to reaction (11):

⅙C₆H₁₂O₆(solid)→CO(gas)+H₂(gas)  (11)

The thermodynamic behavior for the reforming of glucose thus is similarto (even perhaps identical to) that for the reforming of otheroxygenated hydrocarbons having a carbon-to-oxygen ratio of 1:1.

The liquid phase reforming of starch to produce H₂ would first involvethe hydrolysis of starch to form glucose, followed by the reforming ofglucose according to reaction (11). The thermodynamic properties for thehydrolysis reaction can be estimated from the conversion ofdiethyl-ether with water to form ethanol:

C₂H₅OC₂H₅+H₂O→2C₂H₅OH  (12)

The value of ΔG°/RT per mole of ethanol formed in reaction (12) isslightly positive. This slightly unfavorable value, however, is morethan compensated for by the more negative value of ΔG°/RT for reaction(11). Thus, at temperatures above 400 K, the thermodynamic behavior forthe reforming of starch to form H₂ is very favorable. Further still,note that reaction (11) is based on the formation of 1 mole of CO, whilereaction (12) represents the formation of 1 mole of glucose. Therefore,the value of ΔG°/RT for reaction (12) should be divided by 6 forcomparison with the value of ΔG°/RT for reaction (11). This adjustmentmakes the thermodynamic properties for the reforming of starch to formH₂ even more favorable.

Taken in conjunction, the thermodynamic properties presented in FIGS. 2,3, and 4, show that it is possible to conduct the reforming of glucoseand starch at moderate temperatures (e.g., above about 400 K). Thus,steam reforming of carbohydrates in the condensed liquid phase providesa low-temperature alternative to the production of H₂ from petroleum.Furthermore, this low-temperature route for the production of H₂ fromcarbohydrates utilizes a renewable feedstock. This combination oflow-temperature processing and utilization of renewable resources offersa unique opportunity for efficient and environmentally-benign energygeneration.

Reactor System

An illustrative reactor system for carrying out the presently claimedmethod is depicted schematically in FIG. 5. Note that FIG. 5 illustratesan exemplary system. Many other reactor configurations could be utilizedwith equal success.

As shown in FIG. 5, a reactor 18 is disposed within a furnace 20. Liquidreactants are introduced into the reactor 18 via pump 16. As shown inthe figure, the pump 16 is a small-scale, HPLC pump. (FIG. 5 depicts theprototype reactor that was used to conduct the experiments described inExamples 11 and 12.) Obviously, for full-scale hydrogen production, amuch larger pump would be utilized.

Nitrogen supply 10 and hydrogen supply 12 are provided to maintain theoverall pressure of the system and the partial pressure of hydrogenwithin the system chambers in and downstream of the reactor 18. Massflow controllers 14 are provided to regulate the introduction ofnitrogen and hydrogen into the system.

A heat exchanger 22 is provided to reduce the temperature of theproducts exiting the reactor 18. As shown in FIG. 5, the heat exchangeris a water cooler, but any type of heat exchanger will suffice. Theproducts are then swept into separator 24. The design of the separatoris not critical to the function of the invention, so long as itfunctions to separate gaseous products from liquid products. Manysuitable separators to accomplish this function are known in the art,including distillation columns, packed columns, selectively-permeablemembranes, and the like. Pressure regulator 28 and back-pressureregulator 26 serve to monitor and maintain the pressure of the systemwithin the set value or range.

In a typical condensed liquid phase reforming reaction according to thepresent invention, a suitable metal-containing catalyst, preferably ametal catalyst impregnated on a support such as silica, is placed intothe reactor 18. The metal catalyst is then reduced by flowing hydrogenfrom 12 into the reactor at a temperature of roughly 498 K. The pressureof the system is then increased to 300 psig using nitrogen from 10. Thepump 16 is then used to fill the reactor 18 with an aqueous solution ofreactant oxygenated hydrocarbon (for example, sorbitol).

The liquid effluent from the reactor is then cooled in the heatexchanger 22 and combined with nitrogen flowing at the top of theseparator. The gas/liquid effluent is then separated at 24. The productgas stream can then be analyzed by any number of means, with gaschromatography being perhaps the most easily implemented, in-lineanalysis. Likewise, the effluent liquid may also be drained andanalyzed.

One of the primary advantages of the present invention is that it takesplace at greatly reduced temperatures as compared to conventional steamreforming of hydrocarbons. Thus, the inventive method can be optimizedto perform a steam reforming reaction and a WGS reaction simultaneously,in the same reactor, to yield a product comprised almost entirely of H₂,CO₂, and H₂O. This is shown schematically in FIG. 6. Here, asingle-stage reactor 18 is shown, in which the reforming reaction andthe WGS reaction take place simultaneously. The products are then sweptinto a separator 24 (shown in FIG. 6 as a membrane separator) where thehydrogen is separated from the CO₂ and the water. The hydrogen soproduced can be used for any purpose where hydrogen is needed.

Thus, the liquid-phase reforming method of the present inventiongenerally comprises loading a metallic catalyst into a reactor andreducing the metal (if necessary). An aqueous solution of the oxygenatedhydrocarbon is then introduced into the reactor and the solution isreformed in the presence of the catalyst. The pressure within thereactor is kept sufficiently high to maintain the water and oxygenatedhydrocarbon in the condensed liquid phase at the selected temperature.The resulting CO is then converted to additional hydrogen and carbondioxide via a WGS reaction, a reaction that can occur within the samereactor. It is also possible that the catalyst may convert the reactantto CO₂ and H₂ without passing through a CO intermediate. The vapor-phasereforming method of the invention proceeds in essentially the samefashion, with the exception that the reactants are allowed to vaporizeand the reaction takes place in the gas phase, rather than in thecondensed liquid phase.

Oxygenated Hydrocarbons

Oxygenated hydrocarbons that can be used in the present invention arethose that are water-soluble and have at least two carbons. Preferably,the oxygenated hydrocarbon has from 2 to 12 carbon atoms, and morepreferably still from 2 to 6 carbon atoms. Regardless of the number ofcarbon atoms in the oxygenated hydrocarbon, it is much preferred thatthe hydrocarbon has a carbon-to-oxygen ratio of 1:1.

Preferably, the oxygenated hydrocarbon is a water-soluble oxygenatedhydrocarbon selected from the group consisting of ethanediol,ethanedione, glycerol, glyceraldehyde, aldotetroses, aldopentoses,aldohexoses, ketotetroses, ketopentoses, ketohexoses, and alditols. Fromamong the 6-carbon oxygenated hydrocarbons, aldohexoses andcorresponding alditols are preferred, glucose and sorbitol being themost preferred. From among the smaller compounds, ethanediol, glyceroland glyceraldehyde are preferred. Sucrose is the preferred oxygenatedhydrocarbon having more than 6 carbon atoms.

Vapor phase reforming requires that the oxygenated hydrocarbon reactantshave a sufficiently high vapor pressure at the reaction temperature sothat the reactants are in the vapor phase. In particular, the oxygenatedhydrocarbon compounds preferred for use in the vapor phase method of thepresent invention include, but are not limited to, ethanediol, glycerol,and glyceraldehyde. Where the reaction is to take place in the liquidphase, glucose and sorbitol are the most preferred oxygenatedhydrocarbons. Sucrose is also a preferred feedstock for use in theliquid phase.

In the methods of the present invention the oxygenated hydrocarboncompound is combined with water to create an aqueous solution. Thewater-to-carbon ratio in the solution is preferably from about 2:1 toabout 20:1. This range is only the preferred range. Water-to-carbonratios outside this range are included within the scope of thisinvention.

It is much preferred that the water and the oxygenated hydrocarbon arereacted at a pH of from about 4.0 to about 10.0.

Catalysts

As discussed above, the metallic catalyst to be used in the presentmethod may be any system that is capable of cleaving the C—C bonds of agiven oxygenated hydrocarbon compound faster than the C—O bonds of thatcompound under the chosen reaction conditions. Preferably, the metalliccatalyst should have minimal activity toward the cleavage of C—O bonds.Use of a catalyst system having high activity for C—O bond cleavage canresult in the formation of undesired by-products, such as alkanes.

The metallic catalyst systems preferred for use in the present inventioncomprise one or more Group VIII transitional metals, alloys thereof, andmixtures thereof, preferably (although not necessarily) adhered to asupport. From among these metals, the most preferred are nickel,palladium, platinum, ruthenium, rhodium, and iridium, alloys thereof,and mixtures thereof Platinum, ruthenium, and rhodium are the mostpreferred.

The Group VIII transition metal catalyst may optionally be alloyed oradmixed with a metal selected from the group consisting of Group IBmetals, Group IIB metals, and Group VIIb metals. The amount of theseadded metals should not exceed about 30% of the weight of the Group VIIItransition metal catalyst present. The preferred optional metals forinclusion in the catalyst are copper, zinc, and rhenium, alloys thereof,and mixtures thereof

If loaded onto a support, the metallic catalyst should be present in anamount of from about 0.25% to about 50% by total weight of the catalystsystem (the weight of the support being included), with an amount offrom about 1% to 30% by total weight being preferred.

If a support is omitted, the metallic catalyst should be in a veryfinely powdered state, sintered, or in the form of a metallic foam.Where a support is omitted, metal foams are preferred. Metal foams areextremely porous, metallic structures that are reasonably stiff (theyare sold in sheets or blocks). They are very much akin in structure toopen-cell foamed polyurethane. Gas passing through a metal foam isforced through an extremely tortuous path, thus ensuring maximum contactof the reactants with the metal catalyst. Metal foams can be purchasedcommercially from a number of national and international suppliers,including Recemat International B.V. (Krimpen aan den Ijssel, theNetherlands), a company that markets “RECEMAT”-brand metal foam. In theUnited States, a very wide variety of metal foams can be obtained fromReade Advanced Materials (Providence, R.I. and Reno, Nev.).

It is preferred, however, that a support be used. The support should beone that provides a stable platform for the chosen catalyst and thereaction conditions. The supports include, but are not limited to,silica, alumina, zirconia, titania, ceria, carbon, silica-alumina,silica nitride, and boron nitride. Furthermore, nanoporous supports suchas zeolites, carbon nanotubes, or carbon fullerene may be utilized. Fromamong these supports, silica is preferred.

The support may also be treated, as by surface-modification, to removesurface moieties such hydrogen and hydroxyl. Surface hydrogen andhydroxyl groups can cause local pH variations that adversely effectcatalytic efficiency. The support can be modified, for example, bytreating it with a modifier selected from the group consisting ofsilanes, alkali compounds, and alkali earth compounds. The preferredsupport is silica modified by treatment with trimethylethoxysilane.

Particularly useful catalyst systems for the practice of the inventioninclude, but are not limited to: ruthenium supported on silica,palladium supported on silica, iridium supported on silica, platinumsupported on silica, rhodium supported on silica, cobalt supported onsilica, nickel supported on silica, iron supported on silica,nickel-palladium supported on silica, nickel-platinum supported onsilica, and ruthenium-palladium supported on silica. Preferably, thecatalyst system is platinum on silica or ruthenium on silica, witheither of these two metals being further alloyed or admixed with copper,zinc, and/or rhenium.

The catalyst system that is most useful in the reforming reaction of aspecific oxygenated hydrocarbon compound may vary, and can be chosenbased on factors such as overall yield of hydrogen, length of activity,and expense. For example, in testing performed with respect to thevapor-phase reforming of ethanediol, the following results wereobtained. At 250° C., 1 atm., and an H₂O-to-carbon molar ratio of 15, inthe presence of various catalyst systems. where the metal was supportedon silica, the following ranking of metals was obtained in terms ofinitial H₂ yield and stability:

Rh>Ni>Ru>Ir>>Co>>Fe

The catalyst systems of the present invention can be prepared byconventional methods known to those in the art. These methods includeevaporative impregnation techniques, incipient wetting techniques,chemical vapor deposition, magnetron sputtering techniques, and thelike. The method chosen to fabricate the catalyst is not particularlycritical to the function of the invention, with the proviso thatdifferent catalysts will yield different results, depending uponconsiderations such as overall surface area, porosity, etc.

The liquid phase reforming method of the present invention shouldgenerally be carried out at a temperature at which the thermodynamics ofthe proposed reaction are favorable. The pressure selected for thereactions varies with the temperature. For condensed phase liquidreactions, the pressure within the reactor must be sufficient tomaintain the reactants in the condensed liquid phase.

The vapor-phase reforming method of the present invention should becarried out at a temperature where the vapor pressure of the oxygenatedhydrocarbon compound is at least about 0.1 atm (and preferably a gooddeal higher), and the thermodynamics of the reaction are favorable. Thistemperature will vary depending upon the specific oxygenated hydrocarboncompound used, but is generally in the range of 100° C. to 450° C. forreactions taking place in the vapor phase, and more preferably from 100°C. to 300° C. for vapor phase reactions. For reactions taking place inthe condensed liquid phase, the preferred reaction temperature shouldnot exceed 400° C.

The condensed liquid phase method of the present invention may alsooptionally be performed using a salt modifier that increases theactivity and/or stability of the catalyst system. Preferably, themodifier is a water-soluble salt of an alkali or alkali earth metal. Themodified is added to the reactor along with the liquid reactants. It ispreferred that the water-soluble salt is selected from the groupconsisting of an alkali or an alkali earth metal hydroxide, carbonate,nitrate, or chloride salt. If an optional modifier is used, it should bepresent in an amount from about 0.5% to about 10% by weight as comparedto the total weight of the catalyst system used.

EXAMPLES

The following Examples are included solely to provide a more completedisclosure of the subject invention. Thus, the following Examples serveto illuminate the nature of the invention, but do not limit the scope ofthe invention disclosed and claimed herein in any fashion.

In all of the Examples, off-gas streams were analyzed with severaldifferent gas chromatographs (GCs), including a Carle GC with a “PorapakQ”-brand column (Waters Corp., Milford, Mass.) to determine hydrogenconcentrations, an HP 5890 GC with a thermal conductivity detector and a“Porapak N”-brand column (Waters) to determine carbon monoxide, carbondioxide, methane, and ethane concentrations, and the HP 5890 GC with athermal conductivity detector and a “Hayesep D”-brand column (HayesSeparation Inc., Bandera, Tex.) to determine methane, ethane, propane,butane, pentane, and hexane concentrations. Total hydrocarbon and othervolatile oxygenates were determined using an HP 6890 CC with a flameionization detector and an “Innowax”-brand capillary column from AgilentTechnologies, Palo Alto, Calif. (Note: Hewlett Packard's chromatographyoperations were spun off into Agilent Technologies, a wholly independentbusiness, in 1999.)

Example 1

Silica-supported metal catalyst systems were prepared using anevaporative impregnation technique according to the following procedure:(1) Cab-O-Sil EH-5 fumed silica (Cabot Corporation, Woburn, Mass.) wasdried for 24 hours at 393 K; (2) a solution containing the metalcatalyst was added to the silica; and (3) the resulting catalyst wasdried in air.

Example 2

A 4 wt % silica-supported ruthenium catalyst system (Ru/SiO₂) wasprepared according to the general method of Example 1. A ruthenium (III)nitrosyl nitrate solution (1.5 wt % ruthenium solution) was added to thedried silica to produce a 4 wt % Ru/SiO₂ catalyst system. The mixturewas stirred at room temperature for 30 minutes in an evaporation dishfollowed by heating to remove the excess liquid. The resulting catalystsystem was then dried at 393 K in air overnight, and was then storeduntil testing.

Example 3

A 4 wt % silica-supported palladium catalyst system (Pd/SiO₂) wasprepared according to the general method described in Example 1. A 10 wt% tetraamine palladium nitrate solution was diluted with water and thenadded to the dried silica to form a gel upon stirring. The gel was driedat room temperature for one day and further dried at 393 K overnight.The resulting Pd/SiO₂ catalyst system was then calcined in O₂ at 573 Kfor 3 hours.

Example 4

A 4 wt % silica-supported iridium catalyst system (Ir/SiO₂) was preparedaccording to the general method of Example 1. A dihydrogenhexachloroiridate (IV) solution was added to the dried silica to producea 4 wt % Ir/SiO₂ catalyst system. The mixture was then stirred at roomtemperature for 30 minutes in an evaporation dish followed by heating toremove the excess liquid. The catalyst system was dried at 393 K in airovernight, and then stored until testing.

Example 5

A 5 wt % silica-supported platinum catalyst system (Pt/SiO₂) wasprepared through the exchange of Pt(NH₃)₄ ²⁺ with H₊ on the silicasurface. The preparation procedure involved the following steps: (1)Cab-O-Sil EH-5 was exchanged with an aqueous Pt(NH₃)₄(NO₃)₂ solution(Aldrich Chemical, Milwaukee, Wis.) with the degree of exchangecontrolled by adjusting the pH of the silica slurry with an aqueous,basic solution of Pt(NH₃)₄(OH)₂; (2) the resulting material was filteredand washed with deionized water; and (3) and the filtered material wasdried overnight in air at 390 K.

Example 6

Catalyst systems produced using the methods of Examples 1 and 5 wereinvestigated for the vapor-phase reforming of an aqueous ethanediolsolution in the presence of water. In these investigations, 0.1 g of aspecific catalyst system was loaded into a glass reactor and reduced for8 hours at 450° C. in flowing hydrogen before being used. A 10 wt %ethanediol solution in water was introduced via a syringe pump at a rateof 0.2 cc/h to a heated line of flowing helium (100 sccm). The reactionmixture of ethanediol and water was passed through a preheat section tovaporize the aqueous ethanediol solution and then over the catalyst bedat temperatures between 275° C. and 300° C. The partial pressure ofethanediol was 0.001 atm and the water-to-carbon molar ratio was 15 to1.

The resulting gases were analyzed via an online GC equipped with athermal conductivity detector. For these tests, the GC utilized a heliumcarrier gas to maximize the detection of the carbon-containing products.In this mode, it was not possible to detect hydrogen directly, so thehydrogen production was determined indirectly from the amounts of CO,CO₂, and CH₄ produced using the following equations:

1.5 moles of H₂ produced per mole of product CO

2.5 moles of H₂ produced per mole of product CO₂

2.0 moles of H₂ consumed per mole of product CH₄

Table 1 shows the effects of metal type on the conversion of ethanedioland product ratio of the carbon containing products. This table showsthat at 275° C., the ruthenium catalyst system completely converted theethanediol to CO₂, indicating that ruthenium not only effectivelycleaves the C—C bond of ethanediol, but also is an effective WGSreaction catalyst. Ethanediol was also completely converted over boththe platinum and palladium catalyst systems at 275° C., but these metalswere not as effective for the WGS reaction. The iridium catalyst systemwas not as effective for the complete conversion of ethanediol to H₂ at275° C. However, elevating the temperature of the iridium-catalyzedreaction to 300° C. was sufficient to accomplish complete conversion.

TABLE 1 Effect of Catalyst on Steam Reforming of Ethanediol. (Totalpressure = 1 atm, ethanediol partial pressure = 0.001 atm, water:carbonratio = 15.5, GHSV = 72 std liter ethanediol feed per kg catalyst perh.) Carbon Containing Product Temperature Conversion Ratio (%) Catalyst(° C.) (%) CO Methane CO₂ 4% Ru/SiO₂ 275 100 0 0 100 4% Pt/SiO₂ 275 10037.3 0 62.7 4% Pd/SiO₂ 275 100 100 0 0 4% Ir/SiO₂ 300 100 22.2 0 77.8

Example 7

The 4 wt % Ru/SiO₂ catalyst system produced using the method of Example2 was investigated for the vapor-phase reactions of ethanediol in thepresence of water with and without the addition of hydrogen gas in thefeed. In the reactions of this Example, 0.5 g of the catalyst system wasloaded into a glass reactor and reduced for 8 hours at 450° C. inflowing hydrogen before being used. A solution of 10 wt % ethanediol inwater was injected into a heated line and vaporized before the reactorvia a HPLC pump at a rate of 3.6 cc/h. At this feed rate, the gas hourlyspace velocity (GHSV) was 260 std liter of ethanediol per kg catalystper hour. The water-to-carbon molar ratio was 15:1. The vaporizedaqueous solution was then passed over the Ru/SiO₂ catalyst system at atemperature of 300° C. at 1 atm. The liquid product was condensed andthe ethanediol concentration was analyzed via GC.

This same reaction was then repeated verbatim, with the sole exceptionthat hydrogen was added to the feed at a rate of 3 moles hydrogen per 15moles of H₂O per 1 mole of carbon (i.e., 3:15:1, H₂:H₂O:C).

The results are shown in FIG. 7, which shows the conversion ofethanediol as a function of time on stream. Table 2 shows the productratio of the carbon-containing products for this Example at 1 hour andat 117 hours. Table 2 shows that at 1 hour, the primary product was CO₂.After 117 hours of operation, the product ratio to CO₂ decreased with acorresponding increase of the product ratio for CO. FIG. 7 shows thatadding a hydrogen modifier to the reactor decreased the initial activityof the catalyst, but extended the useful operating life of the catalyst.FIG. 7 also shows that the conversion decreased from a high of 94% to74% over the course of 112 hours. Table 2 shows that at 1 hour, CO wasthe primary carbon-containing product and that the product ratio to COincreased as the catalyst deactivated.

TABLE 2 Selectivity for the Steam Reforming of Ethanediol over 4 wt %Ru/SiO₂ at 300° C., 1 atm, and GHSV = 260 std liter of ethanediol per kgcatalyst per h. Time Carbon Containing Product Run On Conversion Ratio(%) Description Stream % CO CO₂ CH₄ CH₃OH No H₂  1 h 98 1.3 96 2.7 0.04No H₂ 117 h 44 45.1 54.8 0.2 0.00 H₂ in Feed  1 h 94 64.2 31.5 4.2 0.04H₂ in Feed  66 h 80 88.5 11.0 0.5 0.00

Example 8

Silica-supported monometallic and bimetallic catalyst systems wereprepared by using the incipient wetting technique to add the given metalto the silica. The preparation procedure involved the following steps:(1) Cab-O-Sil EH-5 fumed silica was dried at 393 K; (2) the metal ormetals were added to the silica by adding dropwise an aqueous solutionof the appropriate metal precursor (approximately 1.5 gram of solutionper gram of catalyst); and (3) the impregnated catalyst was dried at 393K overnight. The catalyst systems were then stored in vials untiltesting.

Example 9

Silica-supported monometallic and bimetallic catalyst systems, made viathe procedure of Example 8, were tested for the vapor-phase reforming ofethanediol (i.e., ethylene glycol). Ten milligrams of a given catalystsystem was loaded into a glass reactor and reduced for 4 hours at 450°C. in flowing hydrogen before use in the reaction. An aqueous solutionof 10-wt % ethanediol in water was introduced via a syringe pump at arate of 0.2 cc/h to a heated line of flowing helium (50 sccm). Thereaction mixture was passed through a preheat section to vaporize theaqueous ethanediol solution and then over the catalyst system at atemperature of 250° C. The partial pressure of ethanediol was 0.0023 atmand the water-to-carbon molar ratio was 15 to 1. The gases were analyzedvia an online GC equipped with a TCD detector. At the low conversions ofthese investigations, CO was the only product detected. Accordingly, theproduction rate of CO was used to characterize both the activity andstability of the different metals. The results are shown in FIGS. 8, 9,10, 11, and 12.

FIG. 8 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, at a molar water-to-carbon ratio of 15 over monometallic catalystsystems containing Rh, Ni, Ru, Ir, Co, or Fe. This graph shows that formonometallic catalysts systems, Rh displays the best activity, followedby, in order of decreasing activity, Ni, Ru, Ir, Co, and Fe. In each ofthe catalyst systems tested, the catalyst contained 1 wt % of the metalon a silica support.

FIG. 9 shows vapor-phase reforming of ethanediol at 250° C. and 1 atm,and a water-to-carbon molar ratio of 15 over two different nickelcatalyst systems (1 wt % Ni/SiO₂ and 15 wt % Ni/MgO—Al₂O₃). These datashow that the metal loading and the support chosen can have significanteffects on catalytic activity. In FIG. 9, the closed circles representmolecules of CO per molecule of metal catalyst per minute for a 1 wt %Ni catalyst on a silica support. The open squares represent molecules ofCO per molecule of metal catalyst per minute for a 15 wt % Ni catalyston MgO—Al₂O₃. Quite clearly, this figure shows that the silica supportis much preferred over the MgO—Al₂O₃ support.

FIG. 10 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, at a water-to-carbon ratio of 15 over a bimetallic catalyst system(Ni—Pd) as compared to monometallic Rh/SiO₂, Pd, and Ni catalystsystems. Here, four distinct catalyst systems were tested: 1.0 wt %Rh/SiO₂, 1Ni—2Pd (0.5 wt % Ni)/SiO₂, 4.0 wt % Pd/SiO₂, and 1.0 wt %Ni/SiO₂. As shown in FIG. 10, the Rh and Ni—Pd catalyst systems had verysimilar activities and stabilities over the course of 7 hours. The Pdcatalyst system had lower activity, but also exhibited a very constantactivity over the course of the study. The Ni catalyst system had verygood initial activity, but exhibited steadily declining activity overthe 7-hour course of the experiment.

FIG. 11 shows the vapor-phase reforming of ethanediol at 250° C. and 1atm, at a water-to-carblon ratio of 15 over various catalyst systems(Rh, Ni—Pt, Pt, and Ni). Here, four distinct catalyst systems weretested: 1.0 wt % Rh/SiO₂, 1Ni—2Pt (0.5 wt % Ni)/SiO₂, 5.0 wt % Pt/SiO₂,and 1.0 wt % Ni/SiO₂. As shown in FIG. 11, the Ni catalyst system againhad good initial activity, but exhibited steadily declining activityover the course of the experiment. The rhodium catalyst system exhibitedhigh and steady activity over the course of the experiment, with themixed Ni—Pt system exhibiting similar stability, but at a lower level ofactivity. The Pt catalyst system exhibited still lower activity and alsoshowed steadily decreasing activity over time.

FIG. 12 shows the vapor-phase. reforming of ethanediol at 250° C. and 1atm, at a water-to-carbon ratio of 15 over various catalyst systems (Rh,Ru—Pd, Pd, and Ru). Here, four distinct catalyst systems were tested:1.0 wt % Rh/SiO₂, 1Ru—2Pd (1.0 wt % Ru)/SiO₂, 4.0 wt % Pt/SiO₂, and 1.5wt % Ru/SiO₂. As in the earlier Examples, the Ru catalyst system againhad good initial activity, but exhibited steadily declining activityover the course of the experiment. The Rh catalyst system exhibited thebest activity, followed by the mixed Ru—Pd catalyst and the Pd catalyst.All three of these catalyst systems exhibited constant activity over thecourse of the experiment.

Example 10

The vapor-phase reforming of sorbitol with either a 1 wt % Rh/SiO₂catalyst system or a 14 wt % Rh/SiO₂ catalyst system, prepared by themethod of Example 1, was carried out at 425° C. and 1 atm, in thepresence hydrogen. For this investigation, a 5 wt % sorbitol solutionwas fed to the system at 7.2 cc/h. One (1) gram of Rh catalyst wasloaded into the reactor and pretreated with flowing hydrogen at 450° C.for 4 h. For this Example, a 5 wt % sorbitol solution was fed to thesystem at 7.2 cc/h and vaporized in either flowing helium or flowinghydrogen. Initially, the 1 wt % Rh/SiO₂ was utilized for the steamreforming of the 5 wt % sorbitol solution in the presence of helium suchthat the He:H₂O:C ratio was 3:32:1. Initially, the catalyst exhibitedcomplete conversion of sorbitol to CO₂ and H₂ over this catalyst. FIG.13 shows the conversion of sorbitol as determined by analyses of thereactor outlet gases. Conversion over 100% is attributed to experimentalerror in measuring flow rates of the partially condensable reactoroutlet gas stream. FIG. 13 shows that after the initially observedcomplete conversion of the sorbitol, the conversion decreased quicklywith time, indicating rapid deactivation of the catalyst.

It was then attempted to reform the 5 wt % sorbitol solution over a 14wt % Rh/SiO₂ catalyst, with H₂ in the feed (H₂:H₂O:C=4/32/1). FIG. 13shows that this 14 wt % Rh/SiO₂ catalyst completely converted thesorbitol for over 80 h of time with no indication of deactivation. GCanalysis confirmed that the major products were carbon dioxide andhydrogen with trace amounts of methane and carbon monoxide.

The 14 wt % Rh/SiO₂ was catalyst was then treated in flowing hydrogenovernight at 450° C. and then used to reform a 10 wt % sorbitol solutionin the presence of helium (He:H₂O:C=3:16:1) at 450° C. FIG. 14 showsthat the 14 wt % Rh/SiO₂ completely converted the sorbitol for over 70h. The helium sweep gas was removed after 70 h, and the catalystcontinued to convert the sorbitol essentially completely. In thisinvestigation, GC analyses showed only carbon dioxide was formed. Thecombined results shown in FIGS. 13 and 14 indicate that higher loadingsof metal enhance the lifetime of the catalyst. These two figures alsosuggest that the silica support may be involved in the deactivationmechanism.

Example 11

A 5 wt % silica-supported platinum catalyst system was made according tothe procedure described in Example 5. The catalyst was, however,modified by dehydroxylation and capping with trimethylethoxysilane. Thecatalyst system was prepared as follows: (1) fumed silica (Cab-O-Sil,EH-5 grade) was dried at 600 K for 10 hours under flowing helium; (2)platinum was added to the support by vapor-phase deposition of Pt(II)acetylacetonate at 500 K; (3) the resulting Pt/SiO₂ catalyst system wascalcined at 600 K in flowing oxygen; (4) the calcined catalyst systemwas reduced at 600 K with flowing hydrogen; (5) the resulting catalystsystem was dehydroxylated under flowing helium at 1173 K; (6) thecatalyst system was treated with CO at 300 K to prevent the platinumsites from reacting with trimethylethoxysilane; (7) the resultingcatalyst was dosed with 4.5 mmol trimethylethoxysilane (Gelest, Inc.,Tullytown, Pa.) at 300 K; (8) the catalyst was dosed with CO until theresidual pressure was 10 torr; (9) trimethylethoxysilane was dosed ontothe catalyst at 473 K; and (10) the resulting catalyst system wascalcined with flowing oxygen at 373 K. The catalyst system contained 70μmol/g of surface platinum as determined by dosing with carbon monoxideat 300 K.

Example 12

Liquid phase reforming of sorbitol was performed using the metalliccatalyst systems described in Examples 5 and 11. The apparatus used forthe reforming is the apparatus depicted schematically in FIG. 5. Thecatalyst was loaded into a ¼ inch stainless steel reactor. The catalystwas reduced by flowing hydrogen across the catalyst at a temperature of225° C. After reduction, the reactor was cooled. The system was thenpurged with nitrogen, and a HPLC pump was used to fill the reactor witha 10 wt % sorbitol aqueous solution. Once liquid was observed in theseparator, the pressure of the system was increased to 300 psig withnitrogen (the pressure is controlled by the backpressure regulator 26;see FIG. 5). While the liquid feed was pumped over the catalyst bed, thefurnace heated the bed to 225° C. The liquid exited the reactor and wascooled in a double-pipe water cooler (FIG. 5, reference number 22). Thefluid from this cooler was combined with the nitrogen flow at the top ofthe cooler and the gas and liquid were separated in the separator 24.

The liquid was drained periodically for analysis, and the vapor streampassed through the back-pressure regulator 26. This off-gas stream wasanalyzed with several different GCs to determine the hydrogenconcentration, the carbon monoxide, carbon dioxide, methane, and ethaneconcentrations, and the methane, ethane, propane, butane, pentane, andhexane concentrations. Total hydrocarbon and other volatile oxygenateswere also determined by GC.

FIG. 15 shows the results for the liquid-phase conversion of a 10 wt %sorbitol solution over, the 5 wt % Pt/SiO₂ catalyst system of Example 5at 225° C. This figure shows the observed turnover frequencies (TOF,moles of product per mole of surface platinum per minute) for CO₂, H₂,and carbon found in paraffins. Additionally, FIG. 15 shows the hydrogenselectivity, which is defined as the observed hydrogen productiondivided by the hydrogen produced from the production of the observed CO₂(13/6 H₂ per CO₂ observed). FIG. 15 shows that 33% CO₂ was observed inthe off-gas. After 22 hours (indicated by the vertical line 10 in FIG.15), the feed was switched to 10% glucose. FIG. 15 shows that theproduction of CO₂ increased without a significant change in the rate ofhydrogen production. Accordingly, the H₂ selectivity decreased to 22%even after accounting for the lower theoretical yield of H₂ from glucose(13/6 H₂ per CO₂ observed).

FIG. 16 shows the result for the liquid-phase conversion of a 10 wt %sorbitol solution at 225° C. over the 5 wt % Pt/SiO₂ catalyst that wasdefunctionalized by capping (see Example 11). This figure shows theobserved turnover frequencies (moles of product per mole of surfaceplatinum per minute) for CO₂, H₂, and carbon found in paraffins.Additionally, this figure shows the H₂ selectivity that again is definedas the observed hydrogen production divided by the hydrogen producedfrom the production of the observed CO₂. FIG. 16 shows that supportingplatinum on the modified silica enhanced both the rates of production ofCO₂ and H₂, as well as the H₂ selectivity. Importantly, this figure alsoshows that when KOH was added to the 10 wt % sorbitol solution, therates of H₂ production increased and the rate of paraffin productiondecreased. Additionally, the H₂ selectivity increased with the additionof KOH in the liquid feed. Importantly, as the KOH concentration isincreased from 0 M KOH to 0.006 M KOH, the H₂ selectivity increased from57% to 77%. In addition, the rate of H₂ production increased from 0.65min⁻¹ to 0.83 min⁻¹. This example clearly demonstrates that thecondensed liquid phase reforming of both glucose and sorbitol ispossible.

The significance of all of the Examples given above is that theydemonstrate that the vapor phrase and condensed liquid phase reformationof oxygenated hydrocarbons to yield hydrogen is possible using a host ofdifferent types of Group VIII metal-containing catalysts.

What is claimed is:
 1. A method of producing hydrogen comprising:reacting water and a water-soluble oxygenated hydrocarbon having atleast two carbon atoms, at a temperature not greater than about 400° C.,at a pressure where the water and the oxygenated hydrocarbon remaincondensed liquids, and in the presence of a metal-containing catalyst,wherein the catalyst comprises a metal selected from the groupconsisting of Group VIII transitional metals, alloys thereof, andmixtures thereof.
 2. The method of claim 1, wherein the catalyst isadhered to a support.
 3. The method of claim 2, wherein the support issurface-modified to remove surface moieties selected from the groupconsisting of hydrogen and hydroxyl.
 4. The method of claim 3, whereinthe support is modified by treating it with a modifier selected from thegroup consisting of silanes, alkali compounds, and alkali earthcompounds.
 5. The method of claim 2, wherein the support is selectedfrom the group consisting of silica, alumina, zirconia, titania, ceria,carbon, silica-alumina, silica nitride, and boron nitride.
 6. The methodof claim 2, wherein the support is silica modified withtrimethylethoxysilane.
 7. The method of claim 2, wherein the support isa zeolite.
 8. The method of claim 2, wherein the support is a carbonnanotube or a carbon fullerene.
 9. The method of claim 2, wherein thesupport is a nanoporous support.
 10. The method of claim 1, furthercomprising reacting the water and the water-soluble oxygenatedhydrocarbon in the presence of a water-soluble salt of an alkali oralkali earth metal.
 11. The method of claim 10, wherein thewater-soluble salt is selected from the group consisting of an alkali oran alkali earth metal hydroxide, carbonate, nitrate, or chloride salt.12. The method of claim 1, wherein the water-soluble oxygenatedhydrocarbon has a carbon-to-oxygen ratio of 1:1.
 13. The method of claim1, wherein the water-soluble oxygenated hydrocarbon has from 2 to 12carbon atoms.
 14. The method of claim 1, wherein the water-solubleoxygenated hydrocarbon is selected from the group consisting ofethanediol, ethanedione, glycerol, glyceraldehyde, aldotetroses,aldopentoses, aldohexoses, ketotetroses, ketopentoses, ketohexoses, andalditols.
 15. The method of claim 1, wherein the water-solubleoxygenated hydrocarbon is selected from the group consisting ofaldohexoses and corresponding alditols.
 16. The method of claim 1,wherein the water-soluble oxygenated hydrocarbon is selected from thegroup consisting of glucose and sorbitol.
 17. The method of claim 1,wherein the water-soluble oxygenated hydrocarbon is sucrose.
 18. Themethod of claim 1, wherein the catalyst comprises a metal selected fromthe group consisting of nickel, palladium, platinum, ruthenium, rhodium,iridium, alloys thereof, and mixtures thereof.
 19. The method of claim1, wherein the catalyst is further alloyed or mixed with a metalselected from the group consisting of Group IB metals, Group IIB metals,and Group VIIb metals.
 20. The method of claim 1, wherein the catalystis further alloyed or mixed with a metal selected from the groupconsisting of copper, zinc, and rhenium.
 21. A method of producinghydrogen comprising: reacting water and a water-soluble oxygenatedhydrocarbon having at least two carbon atoms, in the presence of ametal-containing catalyst, wherein the catalyst comprises a metalselected from the group consisting of Group VIII transitional metals,alloys thereof, and mixtures thereof, and wherein the water-solubleoxygenated hydrocarbon is selected from the group consisting ofethanediol, ethanedione, glycerol, glyceraldehyde, aldotetroses,aldopentoses, aldohexoses, ketotetroses, ketopentoses, ketohexoses andalditols.
 22. The method of claim 21, wherein the catalyst is adhered toa support.
 23. The method of claim 22, wherein the support is selectedfrom the group consisting of silica, alumina, zirconia, titania, ceria,carbon, silica-alumina, silica nitride, and boron nitride.
 24. Themethod of claim 22, wherein the support is surface-modified to removesurface moieties selected from the group consisting of hydrogen andhydroxyl.
 25. The method of claim 22, wherein the support is modified bytreating it with a modifier selected from the group consisting ofsilanes, alkali compounds, and alkali earth compounds.
 26. The method ofclaim 22, wherein the support is silica modified withtrimethylethoxysilane.
 27. The method of claim 22, wherein the supportis a zeolite.
 28. The method of claim 22, wherein the support is acarbon nanotube or a carbon fullerene.
 29. The method of claim 22,wherein the support is a nanoporous support.
 30. The method of claim 21wherein the water-soluble oxygenated hydrocarbon is selected from thegroup consisting of aldohexoses and corresponding alditols.
 31. Themethod of claim 21 wherein the water-soluble oxygenated hydrocarbon isselected from the group consisting of glucose and sorbitol.
 32. Themethod of claim 21 wherein the water-soluble oxygenated hydrocarbon issucrose.
 33. The method of claim 21, wherein the water and theoxygenated hydrocarbon are reacted at a temperature of from about 100°C. to about 300° C.
 34. The method of claim 21, wherein the water andthe oxygenated hydrocarbon are reacted at a pH of from about 4.0 toabout 10.0.
 35. The method of claim 21, wherein the catalyst comprises ametal selected from the group consisting of nickel, palladium, platinum,ruthenium, rhodium, iridium, alloys thereof, and mixtures thereof. 36.The method of claim 21, wherein the catalyst is further alloyed or mixedwith a metal selected from the group consisting of Group IB metals,Group IIB metals, and Group VIIb metals.
 37. The method of claim 21,wherein the catalyst is further alloyed or mixed with a metal selectedfrom the group consisting of copper, zinc, and rhenium.
 38. A method ofproducing hydrogen comprising: reacting water and a water-solubleoxygenated hydrocarbon having at least two carbon atoms, at atemperature of not greater than about 400° C., and at a pressure wherethe water and the oxygenated hydrocarbon remain condensed liquids, inthe presence of a metal-containing catalyst, wherein the catalystcomprises a metal selected from the group consisting of Group VIIItransitional metals, alloys thereof, and mixtures thereof, the catalystbeing adhered to a support.
 39. The method of claim 38, wherein thesupport is selected from the group consisting of silica, alumina,zirconia, titania, ceria, carbon, silica-alumina, silica nitride, andboron nitride, modified to render to remove surface moieties selectedfrom the group consisting of hydrogen and hydroxyl.
 40. The method ofclaim 39, wherein the support is modified by treating it with a modifierselected from the group consisting of silanes, alkali compounds, andalkali earth compounds.
 41. The method of claim 38, wherein the supportis silica modified with trimethylethoxysilane.
 42. The method of claim38, wherein the water-soluble oxygenated hydrocarbon has acarbon-to-oxygen ratio of 1:1.
 43. The method of claim 38, wherein thewater-soluble oxygenated hydrocarbon is selected from the groupconsisting of ethanediol, ethanedione, glycerol, glyceraldehyde,aldotetroses, aldopentoses, aldohexoses, ketotetroses, ketopentoses,ketohexoses, and alditols.
 44. A method of producing hydrogencomprising: reacting water and a water-soluble oxygenated hydrocarbonhaving at least two carbon atoms, in the presence of a metal-containingcatalyst, wherein the catalyst comprises a metal selected from the groupconsisting of Group VIII transitional metals, alloys thereof, andmixtures thereof, and wherein the catalyst is adhered to a supportcomprising a carbon nanotube or a carbon fullerene.
 45. A method ofproducing hydrogen comprising: reacting water and a water-solubleoxygenated hydrocarbon having at least two carbon atoms, in the presenceof a metal-containing catalyst, wherein the catalyst comprises a metalselected from the group consisting of Group VIII transitional metals,alloys thereof, and mixtures thereof, and wherein the catalyst isadhered to a support comprising a nanoporous support.
 46. A method ofproducing hydrogen comprising: reacting water and a water-solubleoxygenated hydrocarbon having at least two carbon atoms, in the presenceof a metal-containing catalyst, wherein the catalyst comprises a metalselected from the group consisting of Group VIII transitional metals,alloys thereof, and mixtures thereof, and wherein the water and theoxygenated hydrocarbon are reacted at a temperature not greater thanabout 400° C., at a pressure where the water and the oxygenatedhydrocarbon remain condensed liquids, and further comprising reactingthe water and the water-soluble hydrocarbon in the presence of awater-soluble salt of an alkali or alkali earth metal.
 47. A method ofproducing hydrogen comprising: reacting water and a water-solubleoxygenated hydrocarbon having at least two carbon atoms, at atemperature of from about 100° C. to about 450° C., and at a pressurewhere the water and the oxygenated hydrocarbon are gaseous, in thepresence of a metal-containing catalyst, wherein the catalyst comprisesa metal selected from the group consisting of Group VIII transitionalmetals, alloys thereof, and mixtures thereof, the catalyst being adheredto a support, and wherein the water-soluble oxygenated hydrocarbon isselected from the group consisting of ethanediol, ethanedione, glycerol,glyceraldehyde, aldotetroses, aldopentoses, ketotetroses, ketopentoses,ketohexoses, and alditols.